In the case of subjecting propylene to gas-phase catalytic partial oxidation with molecular oxygen, thereby producing acrolein and acrylic acid on an industrial scale, various problems are caused. As one of them, it is known that as the temperature to which a complex metal oxide catalyst (hereinafter referred to as “catalyst”) is exposed increase, the deterioration of the catalyst is accelerated. In addition, it is also widely known that when an excessive oxidation reaction is promoted, the yield of a target product is lowered. Then, in order to increase the productivity of a target product under high-load circumstances where a raw material concentration or a space velocity is high, though it is necessary to increase the reaction bath temperature, thereby keeping a reaction rate of the catalyst at a high level, there is involved such a problem that when the reaction bath temperature is high as described above, a catalyst life becomes short. Furthermore, since the gas-phase catalytic partial oxidation of propylene or the like is an exothermic reaction, a local high-temperature portion (hot spot) is generated in a catalyst layer, so that the deterioration of the catalyst and the lowering of the yield become conspicuous. As for these problems, there have been made various proposals in the conventional techniques. For example, Patent Document 1 describes a method in which plural kinds of catalysts differing in occupying volume and calcination temperature, and/or kind and/or amount of alkali metal element from each other, are prepared and filled in a multitubular oxidation reactor in such a manner that the activity increases from the raw material gas inlet toward the outlet in the axial direction of the tube, thereby suppressing a hot spot temperature. This method is aimed to suppress excessive heat generation by filling the catalysts with controlled activity in the inlet side into which the high-concentration raw material gas is introduced. But, in regulating the activity by the occupying volume, there may be the case where a sufficient effect is not obtained because the size of the occupying volume of the catalyst is restricted by a reaction tube diameter; or there may be a possibility that in view of the matter that the catalysts are not uniformly filled, a designed reaction field is not realized, so that a sufficient catalytic performance is not exhibited. In addition, Patent Document 2 describes a method in which a supporting amount of the catalyst is increased from the raw material gas inlet side toward the outlet side to impose a ranking in the catalytic activity, thereby suppressing a hot spot temperature on the raw material gas inlet side, whereas on the outlet side where a highly active catalyst is filled, a gas-phase catalytic partial oxidation reaction is made to reach a conversion of the raw material required from the process standpoint. However, there is involved such a problem that in the catalyst on the raw material gas inlet side where the supporting amount is low, the life is short, whereas in the catalyst on the raw material gas outlet side, the amount of the active component is large, so that the layer of the catalytically active component becomes thick, whereby the reaction heat is accumulated within the catalyst, and the selectivity is lowered. In addition, Patent Document 3 describes a method in which by using annular catalysts, the hot spot temperature is suppressed, thereby making it possible to cope with the reaction under high-load circumstances. But, the annular catalysis also encounter such serious problems that when filled in a multitubular oxidation reactor, it is difficult to uniformly fill the catalysts from the standpoint of properties of the shape; and that from the standpoint of properties of a shaping method, the catalysts collapse or cause powdering because of low mechanical strength, so that not only the reaction tube is plugged, but also the catalytically active component falls down, whereby the catalytic performance is not sufficiently exhibited. Furthermore, Patent Document 4 discloses a technique in which by filling catalysts having a different ratio of bismuth and iron in each reaction tube having two or more reaction zones disposed therein along the axis of the tube in such a manner a total amount of bismuth and iron decreases from the ran material gas inlet toward the outlet, the sublimation of the molybdenum component is suppressed, thereby producing acrolein and acrylic acid stably in high yields over along period of time.